每日科技报告 第29期 Can Math and Science Help Solve Crimes?

sea_star666

Can Math and Science Help Solve Crimes? Scientists Work With Los Angeles Police to Identify and Analyze Crime 'Hotspots'
UCLA's Jeffrey Brantingham works with the Los Angeles Police Departmentto analyze crime patterns. He also studies hunter-gatherers in NorthernTibet. If you tell him his research interests sound completelyunrelated, he will quickly correct you.




"Criminal offenders are essentially hunter-gatherers; they foragefor opportunities to commit crimes," said Brantingham, a UCLA associateprofessor of anthropology. "The behaviors that a hunter-gatherer usesto choose a wildebeest versus a gazelle are the same calculations acriminal uses to choose a Honda versus a Lexus."
Brantingham has been working for years with Andrea Bertozzi, aprofessor of mathematics and director of applied mathematics at UCLA,to apply sophisticated math to urban crime patterns. With theircolleagues, they have built a mathematical model that allows them toanalyze different types of criminal "hotspots" -- areas where manycrimes occur, at least for a time.
They believe their findings apply not only to Los Angeles but tocities worldwide. Their latest research will appear as the coverfeature in the March 2 issue of Proceedings of the National Academy of Sciences (PNAS).Bertozzi spoke about the mathematics of crime at the annual meeting ofthe American Association for the Advancement of Science in San Diego onFeb. 20.
The PNAS ** offers an explanation for when lawenforcement officials can expect crime to be suppressed by intensifiedpolice actions and when crime might merely be displaced to otherneighborhoods.
Crime hotspots come in at least two different types, Brantingham and Bertozzi report in PNAS,along with lead author Martin Short, a UCLA assistant adjunct professorof mathematics, and George Tita, an associate professor of criminology,law and society at UC Irvine. There are hotspots generated by smallspikes in crime that grow ("super-critical hotspots") and hotspotswhere a large spike in crime pulls offenders into a central location("subcritical hotspots"). The two types look the same from the su**ce,but they are not.
Policing actions directed at one type of hotspot will have a very different effect from actions directed at the other type.
"This finding is important because if you want the police tosuppress the hotspot, you want to be able to later take them out andhave the suppression remain," Bertozzi said. "And you can do that withonly one of the two, in the subcritical case."
"Unless you are really looking for them, and our model says youshould, you would not suspect these two types of hotspots," Brantinghamsaid. "Just by mapping crime and looking at hotspots, you will not beable to know whether that is generated by a small variation in crime orby a big spike in crime.
"If you were to send police into a hotspot without knowing whichkind it is, you would not be able to predict whether you will justcause displacement of crime -- moving it somewhere else, which is whatour model predicts if it's a hotspot generated by small fluctuations incrime -- or whether you will actually reduce crime," he said. "Manypeople have argued that adding police to hotspots will just push crimesomewhere else, but that seems not to be true, at least in certaincases. You get displacement in some cases, but not nearly as much asmany people thought."
Drug hotspots and violent crime hotspots have been suppressed, and analysts up until now have not been able to explain why.
In their mathematical model, the scientists are able to predict howeach type of hotspot will respond to increased policing, as well aswhen each type might occur, by a careful mathematical analysisinvolving what is known as bifurcation theory.
"Although this is an idealized model for which all parameters mustbe known precisely in advance in order to make predictions, we believethis is an important step in understanding why some crime hotspots aremerely displaced while others are actually removed by hotspotpolicing," Bertozzi said.
Predicting crime and devising better crime-prevention strategiesrequires "a mechanistic explanation for how and why crime occurs whereit does and when it does," Brantingham said. "We think we have made abig step in the direction of providing at least one core aspect of thatexplanation. We will refine it over time. You need to take theseinitial steps before you can develop new crime-fighting strategies."
Their model, Bertozzi said, "is nonlinear and develops complexpatterns in space and time." These features, she noted, are well knownin related models in other areas of science.
Bertozzi, Brantingham, Short and Tita have been studying crimepatterns in Los Angeles using the last 10 years of data from the LAPDand have been able to identify violent crime hotspots, burglaryhotspots and auto-theft hotspots, among others. They believe theiranalysis likely applies to a wide variety of crimes.
The research is federally funded by the National Science Foundation and the U.S. Department of Defense.
"We have a key to understanding real-world phenomena," Bertozzisaid. "The key is the mathematics. With powerful mathematical tools, wecan borrow methods that have been studied in great detail for otherareas of science and engineering and figure out how to apply them tovery different problems, such as crime patterns."
Will their research actually help police departments reduce crime?
"We're cautiously optimistic," Brantingham said. "Good science isdone in small, incremental steps that can lead to big benefits in thelong term. We are trying to understand the dynamics of crime and tomake small but significant steps in helping our police partners come upwith policing strategies that will help to reduce crime.
"We have to do what biologists and engineers have been doing foryears, which is to try to understand the fundamental mechanics anddynamics of how a system works," he said. "Before you can makepredictions about how the system will behave, you have to understandthe fundamental dynamics. That's true with weather forecasting, whereyou run a climate simulation, and true with crime patterns."
The LAPD is at the world's forefront of knowing where crime is occurring and responding very quickly, Brantingham said.
"Can we actually push policing to look into the future and make areasonable prediction about the near term when deciding how to allocateresources?" Brantingham asked. "This is the type of research that isnecessary to make that a reality."
Why do criminals return to the scene of a crime, or at least the same general area?
"If my house is burglarized today, then it is more likely to beburglarized tomorrow as well," said Short, who has studied problemsinvolving mathematical modeling and pattern formation. "There are goodreasons for repeat victimization, from a criminal's point of view. Theyhave already broken into your house once, so they know how to get in,and they already know what you have in your house. The data back thisup.
"The 'near repeat effect' says not only is my house more likely tobe burglarized again, but so are my neighbors' homes," Short added."The burglar may be comfortable with that area. It may be near where helives."
The scientists are also studying crime patterns with the mathematicsused to forecast earthquakes and their aftershocks. "They are actuallyvery similar," Bertozzi said.
In addition, they have started studying whether patterns of gangviolence in Los Angeles are similar to insurgent killings in Iraq.Bertozzi reported preliminary data on this question at the AAAS meetingon Feb. 20.
"An insurgent who wants to place an improvised explosive device in aparticular location will make the same kind of calculations that a carthief will use in choosing which car to steal," Brantingham said. "Theywant to go into areas where they feel comfortable, where they know thenooks and crannies. They want to be in an area where their activitieswill not appear suspicious. They also want to have a large impact.
"The same thing goes for a burglar trying to break into a house or acar thief or a guy looking for a bar fight," he said. "They want to gowhere they know they can go in and out without seeming too suspiciousand where they can get the biggest bang for their buck. The mathematicsunderlying the insurgent activity and the criminal activity is verymuch the same. We're studying that now."
The researchers have funding from the U.S. Army Research Office's mathematics division to compare Iraq data and gang data.
They have also started a research project with the U.S. Office ofNaval Research to provide mathematical algorithms that can help themextract information from diverse data sets.
Why is an anthropologist collaborating on a mathematical model to analyze human behavior?
"Many social scientists say human behavior and criminal behavior aretoo complex to be explained with a mathematical model," saidBrantingham, who was trained as an archaeologist. "But it's not toocomplex. We're not trying to explain everything, but there are manyaspects of human behavior that are easily understood in a formalmathematical structure. There are regularities to human behavior thatwe can understand mathematically."
"We're not asking whether a particular individual is going to commita crime," Bertozzi said. "We ask whether a particular neighborhood willsee an increase in crime."
It's a matter of group behavior, like studying traffic flow patterns, she said.
"Mathematical models and differential equations have been used inthat field for decades," said Bertozzi, who had not worked with socialscientists before working with Brantingham.
She is interested in applying mathematics to address practical problems that affect peoples' lives.
"This is an exciting area of research," she said. "UCLA has one ofthe top applied mathematics programs in the country, and we are able toattract stellar graduate students, postdoctoral researchers and youngfaculty, such as Martin Short, who have made a huge impact in thisresearch."
Bertozzi and Brantingham began working together after meeting through UCLA's Institute for Pure and Applied Mathematics.
"I knew if we were going to study crime problems, we neededexcellent sources of data," Bertozzi said. "The fact that Jeff had theconnection with LAPD and many interesting classes of problems to studyintrigued me."
Bertozzi and Brantingham, along with George Tita and Lincoln Chayes,a UCLA professor of mathematics, wrote a proposal to the NationalScience Foundation to support the research, which was funded."A lot of what motivated me to look at crime initially was trying totake the approaches to understanding the physical world I learned inarchaeology and applying it to contemporary problems such as crime,"Brantingham said. "With George Tita and others, we reached out to theLAPD, and they have been very supportive of our work."

carryye

有一些想法~~~~~~~~~~~~~~~~~~~~~~~~~~~~~·